Greatly reduced action performance in CS5

Question

The bug issue text below wouldn't fit in the bug report form even though it's less than 2000 characters (another bug, perhaps?)
******BUG******
Concise problem statement:  reduced performance in Action processing in CS5 compared to CS3
Steps to reproduce bug:
1. Create an image file, 8000 by 9880 pixels 16-bit RGB color.
2. The background can be any image, though I was using a scan of a test target with colored patches for scanner calibration.
3.  Create a layer "final target" on top of the background.  Set contents to transparent.
4.  Create a selection 295 pixels on a side with rectangular marquee tool.  Position this selection in the upper left corner.
5.  Save the selection to an alpha channel "Grid Box."
6.  Run an action with the following steps.
a.  Load the selection "Grid Box."
b.  Select the layer "final target"
c.  Expand the selection 2 pixels.
d.  Fill the selection with the foreground color.
e.  Set the foreground color to white.
f.  Select the background layer.
g.  Move the selection 295 pixels to the right.
h.  Save the new selection as "Grid Box", replacing the channel.
The use of this action:
Use the eyedropper tool to select a color from the center of the selected square, then use the magic wand tool to subtract from the selection using the color in the center of the square in contiguous mode with tolerance set to 8.  Then run the action, and repeat the above process in the next selected square.  In the scan I am preparing, there is a grid of colored squares surrounded by a large black border.  The final result needs the black border eliminated so that the colored squares completely butt up against each other spaced 295 pixels apart.
So by running the action, the color in the center of each box is copied to fill the rest of the square selected area that's black, leaving the center portion intact.   The copied colors go on the "final target" layer so the background layer is not disturbed.
If you need a copy of the action and/or the image file, contact me by email.
Results:  In CS5 the action is unusable due to the long run time.
Expected results:  In CS3 it works perfectly.

Answer 1

My theory initially was that you had given Photoshop just enough RAM to work efficiently with your CS3 setup, but perhaps because of differences in your Photoshop RAM setting or perhaps because Photoshop CS5 has more code in memory, it's starving for RAM under the same test, and goes to its scratch file for relief.
I created a test image and tried your action with a stopwatch.
Photoshop CS5 x64 on Windows 7 x64 (i.e., with plenty of RAM) takes 1.8 seconds to run through your action.
Photoshop CS5 32 bit consistently takes 6.8 seconds to go through the same steps.   Notably it stalls on the Expand and Select layer "Background" steps for a few seconds each, where it blazed right through them in the 64 bit version.
In my case I have given Photoshop CS5 2897 MB to work with (89%).  This number is larger on a 64 bit system than what you can set because Photoshop 32 bit can use up to a 3 GB address space.
I'll do tests next with earlier versions of Photoshop.
-Noel